Pump station flowmeter

ABSTRACT

A pump station flowmeter is disclosed including a pump status comparator for creating level status without being connected to any level sensors by comparing pump status to a list of association between expected pump status and levels. The wet well dimension, pump status signals, clock signals, level status are recorded in memory before being used as input to a flow calculator which calculates inflow and outflow. A flow rectifier readjusts the inflow and outflow according to a variable proportion of the difference between an average of many outflows and one outflow, and using this difference to readjust a variable tolerance and the variable proportion. This optimizes accuracy according to each specific installation. Abnormal pump operations are confirmed when a predetermined number of possible abnormal pump operations occur in a row are detected by comparing the outflow to the average of many outflows plus or minus the variable tolerance. A maintenance status is declared when an outflow calculated is physically impossible so the inflow calculated is the time of operation of the pumps divided by the time of the maintenance status. Alarms are generated when the outflow or the inflow is over or under predetermined values. Outflow can be replaced by a coefficient if the wet well dimension is unknown so the flowmeter can still be used to generate alarms.

BACKGROUND

1. Field of Invention

A pump station flowmeter is disclosed which includes a volumetricflowmeter for determining an accurate measurement of the flow of liquidthrough a liquid system like a sewage system, a pump status converterfor eliminating the usual heavy modification of the control panelrequired by the installation of volumetric flowmeters, a flow rectifierto calculate flow with maximum accuracy according to each specificinstallation, an abnormal pump operation processor to differentiate pumpflow error calculation from real abnormal pump operation, and a pumpflow variation alarm gate for generating alarms when abnormal pump flowis calculated based only on pump-on and pump-off inputs.

2. Description of Prior Art

Most Prior Art is related to volumetric flowmeters specially designedfor pump stations. They require level inputs to work. None calculatesflow without being connected to level sensors, none individuallyoptimizes its calculus for each specific installation, and none is ableto generate pump flow variation alarms without any inputs other thanpump-on and pump-off.

Pump station flowmeters, or the like, are well known in the patentedprior art, such as the U.S. Pat. Nos.: Martig, Jr. 4,127,030, Jorritsma4,455,870, 4,669,308 and 4,821,580; Olsson 4,467,657, Free et al.4,897,797, Hon 4,856,343, Adney 4,962,666, and Marsh et al. 5,313,842and 5,385,056

(a) All the instruments using these patents must be physically connectedto level sensors and/or pressure devices in order to be used. This makesthe installation of these instruments laborious and expensive.

Pump stations are composed of a wet well which accepts liquid inflow andtemporarily stores such inflow, and a pump, or combination of pumps,which discharge the accumulated liquid from the wet well. The rate ofchange of level in the wet well with respect to time (dl/dt) is afunction of the shape and size of the wet well, the flow entering thewet well is the inflow, and the flow leaving the wet well is theoutflow.

The shape and size of the wet well are usually known, and therefore ifdl/dt is measured, it can be converted to the rate of change of volumewith respect to time (dV/dt). The rate of change of volume depends onthe inflow and outflow.

While the pump (or pumps) is off, the inflow can be measured by timinghow long it takes for the liquid to fill a known volume. This is done byusing existing upper and lower limit switches which are already presentto turn the pumps on and off. This method provides an average inflow(Inflow) over the time that it takes to fill the known wet well volume.

If the Inflow is also known during the pump on time, the total volumepassed through the wet well in one wet well pump cycle can be calculatedby the equation: Outflow=Vp/tp+Inflow.Outflow is the average outflow ofthe pump in operation for that cycle, Vp is the volume of the wet wellbetween the pump on and pump-off switches, and tp is the length of timethe pumps were on. It is important to note that the inflow is a functionof time and is not a constant. If an Inflow for the pump-on time isknown, then a numerical version of equation Outflow=Vp/tp+Inflow wouldbe used:

    Volume/cycle=Vp+Inflow×tp.

(b) Unfortunately, timing the wet well as it fills will give an Inflowwhich is not an accurate estimate of inflow during the pump on time ifthe inflow significantly increases or decreases between the pump offtime and pump on time. One way to reduce this error is to add anotherlevel switch at an intermediate level to define another, smaller volume.The fill time of this intermediate volume can be used to measure anInflow over a shorter period of time which is closer to the onset of thepump-on time, and, hence, is a better estimate of the Inflow during thepump on time.

Variations on this idea include measuring the Inflow before and afterthe pump on time and calculating their average which is Inflow, oradding more intermediate level switches to measure several Inflows andthen performing a best fit of the Inflow versus time for interpolationand averaging. Although these techniques improve the system'sperformance, a sudden flow change will still lead to large errors, andthe installation process becomes impractical.

(c) Inflow changing at a high frequency can cause large errors in theflow calculus. High frequency inflows are flows which change asignificant amount over a short period of time, making it difficult fora system which samples the flow periodically to obtain an accurateestimate of the inflow during the pump-on time. High frequency flows arelikely to occur at pump stations downstream of another pump station orat industrial pump stations. Small domestic pump stations may have highfrequency phenomena as well.

A method disclosed in the Jorritsma U.S. Pat. No. 4,455,870 samples theinflow once per pump cycle, and a second method samples the inflow twiceper pump cycle, and therefore, it was thought to be twice as accurate asthe first method. Adding more intermediate switches allows a system tomeasure the volume through the wet well accurately at even higher inflowfrequencies. However, it is not practical to measure high frequencyinflows in this manner because too many switches are required, and theerrors related to the sensors themselves add-up.

(d) One important phenomenon of periodic flow entering a pump stationcan be termed "lock-on". Lock-on occurs when the pump-on time and theinflow synchronize and remain that way which means the liquid is goingin at about the same speed it is going out. Lock-on maximizes the errorsin flow measurement systems which use fill times to estimate the inflowduring the pump on time. The occurrence of lock on is affected by thesize of the wet well, the inflow frequency, the inflow magnitude, andthe pump characteristics. It occurs very easily over a relatively widerange of frequencies. Such frequency conditions often exist downstreamof another pump station or at relatively small pump stations.

Once a pump station is locked on, it will remain so until the inflowfrequency changes enough to disturb it. The tendency of the pump-on timeand the maximum inflow to remain locked in phase can be explained asfollows. At low inflows, the pump is less likely to come on because thelevel is less likely to reach the top level switch. Conversely, the pumpis more likely to come on when the inflow is high. This tendency forcesthe pump to turn on during the increasing part of the inflow cycle. Thepump-on time lengthens because of the increasing inflow. Ultimately, thepump-on time straddles and then passes the inflow peak. Once the pump ontime occurs during the period of decreasing inflow, the pump flow islarge enough to empty the wet well before the inflow reaches itsminimum. At this point, the two cycles are locked in phase and thepump-on time will not advance across the inflow minimum. Under theseconditions, inflow estimates based on prior fill time data will behighly inaccurate.

(e) These problems are partially overcome by using a different approach.If the outflow of the pump (or pumps) and the time of operation of thepumps are known, the volume passing through the wet well in one pumpcycle can be calculated by: Volume per cycle =pump outflow×time ofoperation. The filling time of the well being known, the Inflow of acycle can be calculated by: Inflow=volume per cycle/(time ofoperation+filling time).

In most cases, wet well pumps discharge into an open channel pipe whichcarries the liquid downstream by gravity: the pumps simply lift thewater a constant distance from the pump outlet to the elevation of theopen channel pipe. The pump outlet is under a constant pressure due tothe column of water between the pump outlet and the beginning of theopen channel flow line where the liquid discharges to a gravity feedline. The pressure on the inlet side of the pump is directly related tothe level of the liquid in the wet well. The liquid level changes fromthe pump stop level to the start level to the stop level at each cycle.Each level being reached at each cycle, we can conclude that a constantaverage pressure generates a constant average pump outflow. If theinflow is accurately calculated, the outflow calculated will be fairlyconstant. If the calculated outflow is not constant, we can assume twopossibilities: the inflow was not properly calculated or the pumpoutflow had really changed.

Marsh U.S. Pat. No. 5,385,056 assume only the first possibility bycomparing the last calculated Outflow of a pump to the average of allthe Outflow for that pump which is Outflow. If the Outflow is within aspecified range of Outflow, then Outflow is updated with Outflow. If theOutflow calculated is outside the specified range, then Outflow is usedinstead of the last Outflow. The possibility that an outflow can changedrastically, like when a pump is damaged or blocked was not considered.It is more accurate to say that the exact Outflow is somewhere betweenthe last calculated Outflow and Outflow.

Furthermore, they assume that by adding intermediate levels, they wouldgain accuracy. Level sensors operating in pump stations wetwell arerarely highly accurate due to turbulent liquid surface, grease build-up,solids, etc. Adding levels means less distance between levels. Reducingthe distance between levels by two is like doubling the resulting sensorrelated error. For example, let's say a station using float switches hasan accuracy of 1/2 inch each. Two sensors are necessary to calculate avolume. If 20 inches separates the 2 switches, then the error is 5%(1/2×2/20"). If an intermediate switch is installed 8 inches from thetop switch, the error becomes 12.5% (1/2×2/8").

(f) Each pump station being different with its own filling and emptyingcharacteristics, a specific range, common to all stations can notgenerate the most accurate values for all stations. The station'scharacteristics change over time, ruling out the possibility of using aspecific range even within a station as specified in Marsh U.S. Pat. No.5,385,056.

(g) The stability of the outflow calculated for each pump, which iscalculated using the inflow, is a proof of the accuracy of the inflow.Two reasons can create rapid outflow changes that could let us believethe inflow causes the errors in the calculation. One is natural, meaninginhuman factors cause it, and one is human, meaning the level sensors orthe pumps are manually activated because the pump station is in a periodof maintenance. Usually in a period of maintenance, the wet well iscleaned using high pressure water. This makes the level detector,specially if floats are used, send false signals to the control panelwhich starts and stops the pumps at any level at any time. This induceserrors in the volumetric flowmeter which understands that the start andstop levels were reached in a matter of seconds generating giganticinflow and outflow. The maintenance people might turn the pump off or onto determine if they are working properly, which gives the impressionthat the starting or stopping levels were reached. None of the abovepatents have any way to detect that a pump station is in a maintenanceperiod.

(h) All the above volumetric methods calculate flow using functions thatassume a constant Inflow or average outflow. The real inflow enteringthe pump station is always changing. This fact invalidates the uses of aconstant inflow calculation as an acceptable representation of reality.

(i) Most of the instruments using the above volumetric methods generatealarms based on low or high pump outflow which indicate a pump problem.To do this, the minimum information supplied by the user to theinstrument is the geometry of the well, and the instrument must beconnected to the level sensors. They can not generate abnormal pump flowalarms without them. It is not practical for a pump manufacturer tointegrate in its pumps an outflow alarm system without knowing if theend user will be able to provide the wet well geometry and the levelsensors.

(j) No Prior Art shows how to calculate inflow and outflow when a pumpis continuously running and when more than one pump is running.

(k) This device can be used in any installation that has a mechanismthat changes its state at set levels. This apparatus can facilitate theinstallation of instruments that need to know the level to operate.Volumetric flowmeters are good examples of these instruments. Thisapparatus reduces installation time of such instrument from hours tominutes by reducing or eliminating the necessary modification of thecontrol panel of the pump station.

The present invention was developed to avoid the above and otherdrawbacks of the prior systems.

OBJECTS AND ADVANTAGES

Accordingly, several objects and advantages of my invention are:

(a) to provide a pump station flowmeter that can be installed withoutbeing connected to any level sensor, reducing the cost of installation;

(b) to provide a pump station flowmeter that reduces the pump on timeinflow and outflow errors without the use of additional or existinglevel sensors;

(c) to provide a pump station flowmeter that accurately calculatesflows, even when inflow changes rapidly without the use of additional orexisting level sensors;

(d) to provide a pump station flowmeter that calculates accurately whenthe "lock-on" phenomenon occurs;

(e) to provide a pump station flowmeter that discerns outflowcalculation errors from abnormal pump operation;

(f) to provide a pump station flowmeter that continuously self adjustsits parameters to optimize the accuracy for each individual station;

(g) To provide a flowmeter which can identify when a pump station is inmaintenance period.

(h) to provide a pump station flowmeter that calculates inflow using afunction representing the time changing reality;

(i) to provide a pump station flowmeter that can generate abnormal pumpflow alarms, even without supplying the wet well geometry or beingconnected to the level sensors;

(j) to provide a pump station flowmeter that calculates inflow andoutflow when a pump is continuously running and when more than one pumpis running.

(k) to provide to other instruments the level data they need withoutbeing connected to any level sensor.

Further objects and advantages of my invention will become apparent froma consideration of the drawings and ensuing description.

DRAWING FIGURES

FIG. 1 is a diagrammatic representation of a wet well pumping system;

FIG. 2 is a schematic of the basic operation of a wet well pumpingsystem in reference to time;

FIG. 3 is a graph of 4 pump cycles showing inflow calculated using theaverage method;

FIG. 4 is a graph of 4 pump cycles showing inflow calculated using afunction of the inflow and time f(t);

FIG. 5 is a graph of 4 pump cycles comparing the results of the averagemethod and the function f(t);

FIG. 6 is a graph of 4 pump cycles showing inflow calculated using theaverage method in which a peak inflow is reached;

FIG. 7 is a graph of 4 pump cycles showing inflow calculated using thefunction f(t) in which a peak inflow is reached;

FIG. 8 is a graph of 4 pump cycles comparing the results of the averagemethod and the function f(t) in which a peak inflow is reached;

FIG. 9 is a block diagram of a basic embodiment of the present inventionusing a pump status converter, a flow rectifier, an abnormal pumpoperation processor, and a flow variation alarm gate;

FIG. 10 is a block diagram of a pump status converter;

FIG. 11 is a schematic of pump operation and level activation inreference to time for a pump station having 3 pumps;

Reference Numerals In Drawings

20 Liquid in wet well

22 Inflow source of liquid

24 Wet well

26 Start level

28 Pump status

30 Outlet of liquid

32 Stop level

34 Control panel

36 Pump cycle

38 Liquid level

40 Volume between levels

42 Inflow over pump OFF period

44 Inflow from average formula

46 Inflow curve from Inflow(t) formula

48 Inflow from Inflow(t)formula

50 Operating configuration

52 Pump status converter

54 Clock

56 Raw data memory

58 Flow calculator

60 Data storage memory

62 Flow rectifier

64 Under counter

66 Over counter

68 Reset counter means

70 Maintenance gate

72 Abnormal event gate

74 Inflow alarm gate

78 Outflow alarm gate

80 Operation sequence memory

82 Association sequence

84 Association sequence comparator

86 Level memory

88 Level gate

90 Delay calculator

92 Sequence analyzer

94 Pump status list

96 External flowmeter

DESCRIPTION OF INVENTION

FIG. 1 illustrates by a diagram a wet well pumping system, commonlycalled a pump station, in which a liquid 20 from inflow source 22 fillsa wet well 24 until a level sensor 26 starts a pump or combination ofpumps 28 to pump out the liquid through an outlet 30 until a levelsensor 32 stops the pump or combination of pumps. Throughout thefollowing text, a pump equals one or more pumps. The source 22 fills thewet well 24 at a variable filling rate, or inflow. A pumping rate, oroutflow, is usually constant for a pump, but not always, so it can notbe assumed to be a constant value. An electric control panel 34 receivesa signal from a level sensor system (26 & 32) when the start and stoplevels are reached, then starts or stops the pump 28 according to anoperating configuration specifying an operating sequence related to thepump operation when different levels are reached.

The level sensor system can be a float switch system, an ultrasonicsystem, a pressure system, a resistive system, a capacitive system orany other type of system supplying a level signal to the control panel34 when specific levels are reached. A control panel 34 is usuallydesigned to control two or more pumps and supply the user withinformation such as pump status, current, cumulative operation time,level of the liquid, etc. The operating sequence can be altered by humanfactors, like a user manually starting or stopping the pumps, andabnormal factors, like a defective pump.

FIG. 2 illustrates the basic operation of the pump station described inFIG. 1 in relation to time. A pump cycle 36 is a repetition of the stepsdescribe in FIG. 1. A pump cycle 36 begins when the pump stops when stoplevel 32 is reached. A liquid level 38 rises from the stop level 32 to astart level 26. A volume of liquid 40 between the start level 26 and thestop level 32 is known. The volume between levels 40 is constant andused in the following equations to calculate an inflow. A fill up timebetween pump operation D1 is calculated by subtracting t2 from t1. Anaverage inflow D1 for the period t1 to t2 is calculated by: ##EQU1##

The same applies to period ##EQU2##

This is true only if no pump runs while D1, D2, D3 or D4 are calculated.But sometimes, pump stations operate in a condition where a pump p isalmost always running and a second pump operates from a higher level. Inthis case, the outflow generated by the pump p is added to the value ofthe inflow. The pump p is usually running between lower levels at whichan average outflow of p (Outflow(p)) was calculated when the pump wasstopping from time to time. The average level at which the Outflow(p) iscalculated directly influences its value: The higher the level, thehigher the value. When a pump is almost always running, the averagelevel of operation between the starts and stops of the second pump ishigher, meaning the Outflow of the pump that is always running ishigher. A coefficient Kp adjusts the value of Outflow(p) according tothe difference of performance of the pump p due to an operation at adifferent average level. To calculate Inflows for D1, D2, D3 or D4 whilea pump p is running, the following equations 1, 2, 3 and 4 apply:##EQU3##

The volume between levels 40 and the time are the only accurate basicinformation used by the present invention to calculate accurate inflowand outflow. When the pump is not in operation, an accurate Inflow iscalculated.

FIG. 3 to FIG. 8 shows why an equation calculating a curve representsmore accurately the reality continually changing rate of an inflow. FIG.3 to FIG. 5 and FIG. 6 to FIG. 8 represent 2 examples of continuallychanging rate of an inflow over a period of 4 cycles.

FIG. 3 is a graph showing inflow calculated using an average method. Itrepresents 4 cycles of a pump station in which the inflow rate hadchanged over time. An accurate Inflow 42 is calculated for each periodt1-t2, t3-t4, t5-t6 and t7-t8 in which the pump are not in operation.D1=Inflow of period t1-t2, D2=Inflow of period t3-t4, D3=Inflow ofperiod t5-t6, and D=Inflow of period t7-t8. Knowing the accurate volumebetween levels 40 and the accurate time at which the levels are reached,the Inflow is therefore accurate.

A method of calculating inflow while the pump is running is toextrapolate the last calculated inflow in the pump running period t2-t3,t4-t5 and t6-t7. Extrapolating assumes a non changing rate of inflowover time which is a highly unfair representation of reality, so it wasnot included with the drawings. FIG. 3 shows a more accurate, but notperfect method of calculating inflow while the pump is running. Itcalculates an average 44 of the inflow (Inflow) for the period beforeand after the pump operation period which is ##EQU4## and so on for theother cycles. Averaging assumes a fixed changing rate of inflow overtime which is not a fair representation of reality either. It appearsaccurate that the inflow at one time is somewhere between the inflowbefore and after that time, but if the time was a peak and inflow beforeand after were calculated on each side of it, then assuming the averageof the inflow before and after represents the flow at this time iswrong.

FIG. 4 is a graph of 4 pump cycles showing an inflow calculated using afunction which generates a curve of the inflow and time f(t). Itrepresents the same cycles as FIG. 3 using a function Inflow(t) of theinflow in relation to time that uses the trend on the inflow over 4cycles, which is over 4 Inflow calculations. The curve 46 representsInflow(t) created using the Inflow of the period D1, D2, D3 and D4.Averages 48 are extracted from Inflow(t).

FIG. 5 is a graph of 4 pump cycles comparing the results of the averagemethod, explained in FIG. 3, and the function Inflow(t), explained inFIG. 4. It compares the averages 44 calculated with the average methodand the averages 48 calculated with Inflow(t). The difference, betweenthe averages 44 and 48 for each period of pump running, is related tothe variation of the inflow during these period.

FIG. 6 is a graph of 4 pump cycles showing inflow calculated using theaverage method in which a peak inflow is reached.

FIG. 7 is a graph of 4 pump cycles showing an inflow calculated using afunction which generates a curve of the inflow and time f(t). Itrepresents the same cycles as FIG. 6 using a function Inflow(t) of theinflow in relation to time that uses the trend on the inflow over 4cycles, which is over 4 Inflow calculations.

The curve 46 represents Inflow(t) created using the Inflow of the periodD1, D2, D3 and D4. Averages 48 are extracted from Inflow(t).

FIG. 8 is a graph of 4 pump cycles comparing the results of the averagemethod and the function Inflow(t) in which a peak inflow is reached. Itcompares the averages 44 calculated with the average method and theaverages 48 calculated from Inflow(t) for the same cycles as FIG. 6 andFIG. 7. The difference between the averages 44 and 48 for each period ofpump operation, becomes large when a peak is present. To increase theaccuracy of the curve, only the middle on the curve, between t4 and t5,is used. Every time a new Inflow can be calculated, a new Inflow(t) iscalculated and only the middle portion is used because it is the mostaccurate portion of Inflow(t).

The result of the following equation 5 is Inflow(t).

    Inflow(t)=at.sup.3 +bt.sup.2 +ct+d

The function Inflow(t) is a curve with two possible changes ofdirection. This formula gives a function in which the average of eachinterval is equal to the Inflow used to calculate it.

This means: ##EQU5##

Inflow(t) is extracted by following these steps: ##EQU6##

It is the same for the 3 other intervals: ##EQU7##

It gives 4 equations with 4 unknowns that can be resolved to find thevalues of a, b, c and d of the function Inflow(t)=at³ +bt² +ct+d.

If a flow calculator is not powerful enough to use this sophisticatedfunction, the following less accurate, but still usable functions can beused where ##EQU8##

An Outflow represents the average of a plurality of Outflows.

The liquid level in the wet well directly affects the performance, oroutflow, of the pump. The higher the level, the better the performance.The lower the level, the lower the performance. If the liquid levelstays higher for more than half the pumping time, then it is expected tocalculate an Outflow higher than the Outflow. If the liquid level stayslower for more than half the pumping time, then it is expected tocalculate an Outflow lower than the Outflow. Outflow is accurate only ifthe period in which the liquid level is high is as long as the period inwhich the liquid level is low in the pumping time. Inflow(t) is alsoused to figure out the liquid level while the pump is running.

FIG. 9 is a block diagram of a basic embodiment of the present inventionusing a pump status converter, a flow rectifier, a maintenance gate, anabnormal event gate, and flow variation alarm gates. The block diagramof FIG. 9 discloses a system, according to the present invention, forobtaining accurate outflow and inflow by using solely the pump 28 statusfrom the basic apparatus described in FIG. 1 operating according to FIG.2, and time. The user supplies the volume between levels 40 and theoperating configuration 50 to a pump status convertor 52, if the pumpstation operates differently than the one described in FIG. 2. If theuser does not supply the volume 40, the present invention can stillgenerate alarms based on variation of the pump outflow.

A clock 54 generates the time at which the pump status 28 is changing.The pump status is also used to identify the pump for which an outflowis calculated and its associated time. The time and the pump status canoptionally be recorded in a data storage memory 60 for later processing.The pump status and its related time of occurrence is transmitted to apump status converter 52. The pump status converter 52 generates thestart levels status and stop levels status from the pump status 28 andthe operating configuration 50. This information is recorded in a rawdata memory 56. A flow calculator 58 calculates Inflow(t), and Outflowof the pump in operation between the time t4 and t5 as described in FIG.2. Equation 6 extracts from Inflow(t) the Inflow for the period t4 tot5. Outflow is calculated using equation 7. ##EQU9##

To achieve the maximum accuracy for each individual pump stationinstallation, the following hypotheses are assumed:

a) An outflow for a pump varies slowly over time, unless an abnormalcondition occurs;

b) An inflow varies rapidly; therefore the difference between realityand the calculated inflow can be high;

c) An average of Outflow calculated over many cycles, Outflow, isusually accurate, unless an abnormal condition occurs;

d) The real outflow for a pump is somewhere between Outflow and Outflow,unless an abnormal condition occurs.

e) An Outflow is influenced by the average liquid level for the periodat which Outflow is calculated.

A flow rectifier 62 is used to cross check the accuracy of the Outflowand Inflow according to the preceding hypotheses in which an average ofOutflow is calculated using many Outflow, an acceptable differencebetween Outflow and Outflow is considered, adjusted and applied, and anadjustment is made to Outflow to reflect the average liquid level forthe period at which Outflow is calculated.

A variable tolerance refers to an acceptable percentage of differencebetween the Outflow and the Outflow. The variable tolerance is increasedif Outflow is too close to the limit of Outflow±the variable toleranceor if it exceeds it. The variable tolerance is reduced if Outflow iscloser to Outflow than the limit of Outflow±the variable tolerance. TheOutflow is used to update Outflow. A proportion of accuracy factor isused to specify where the real outflow is between Outflow and Outflow.The function Inflow(t) is used to calculate at which average liquidlevel Outflow was calculated and affect the proportion of accuracyfactor accordingly. If the Outflow calculated is within the range ofOutflow±the variable tolerance, then the proportion of accuracy factorwill be different than if Outflow was outside the variable tolerance.The proportion of accuracy is always applied to readjust the values ofInflow and Outflow according to the following equations 8 and 9:

    Accurate Inflow=Inflow+(Outflow-Outflow)×proportion  (8)

    Accurate Outflow=Outflow+(Outflow-Outflow)×proportion (9)

The flow rectifier 62 gives accurate results if the station is operatingnormally, but can not discern errors in calculation from abnormal pumpoperation. A combination of counters and gates determine if the results,calculated when the pump is in operation, are right or wrong. An eventis composed of the pump status, the start and stop time of the pump, theInflow, the Outflow and the Outflow for the period included between thestart and stop time. Variation determining means illustrated as underand over counters 64, 66 is provided responsive to the flow rectifier 62for determining the occurrence of a variation between the averageemptying characteristic and a predetermined tolerance, and tagging thelevel status signal, the timing signal, and the volume signal used tocalculate the emptying characteristic as being a possible abnormalevent.

An under counter 64 is increasing each time Outflow is lower thanOutflow minus the variable tolerance. When this occurs, the undercounter 64 tags the events used to calculate Outflow as being possiblyabnormal events.

An over counter 66 is increasing each time Outflow is higher thanOutflow added to the variable tolerance. When this occurs, the overcounter 66 tags the events used to calculate Outflow as being possiblyabnormal events.

A reset means 68 resets the under counter 64 when the over counter 66increases, and resets the over counter 66 when the under counter 64increases. It untags the possible abnormal events tagged by the undercounter 64 when the over counter 66 increases, and untags the possibleabnormal events tagged by the over counter 66 when the under counter 64increases. It resets both counters and untags all possible abnormalevents tagged by both counters when the Outflow is within Outflow ±thevariable tolerance.

A maintenance gate 70 operates when Outflow is higher than apredetermined maximum outflow representing an outflow that could not beachieved under the best conditions. When the Outflow is higher than thepredetermined maximum outflow, it resets both counters (64 and 66) anduntags the possible abnormal events tagged by both counters (64 and 66).It calculates the time of operation of the maintenance gate 70 and thecumulative time of operation of the pump during the operation of themaintenance gate 70. It calculates the total flow through wet well usingthe Outflow multiplied by the time of operation of pump. It calculatesthe average inflow for the time in which the maintenance gate 70 is inoperation by dividing the total flow through wet well by the time ofoperation of the maintenance gate 70. Then it generates a maintenancestatus signal.

An abnormal event gate 72 is used when one of the counters (64 or 66)increases. It operates when one of the counters (64 or 66) is higherthan a predetermined value representing the number of possible abnormalevents necessary to become confirmed abnormal events. It recalculatesthe Outflow from the time of the first tagged possible abnormal eventthen reprocesses the information recorded in the raw data memory 56 fromthe time of the first tagged possible abnormal event using the newlycalculated Outflow when necessary. When the abnormal event gate 72 isnot in operation, it records the time of the first tagged possibleabnormal event in its memory, then tells the flow calculator 58 to reada new event from the raw data memory 56.

The data can be used to calculate other valuable information like volumethrough the wet well, pump's outflow and combination of pump's outflow.Most pump stations are designed to accept a certain inflow, and aspecific outflow is expected for each pump and combination of pumps. Aninflow alarm gate 7,4 can be set to generate an alarm when the Inflow isoutside a preset maximum and minimum inflow or a maximum flow variation.An outflow alarm gate 7,6 can be set to generate an alarm when theOutflow is outside a preset maximum and minimum outflow or a maximumvariation flow for each possible combination of pumps.

It is sometimes difficult or impossible for a user to know the volumebetween levels in the wet well, but the user might want to know if thepump is performing as expected. Most pump stations are designed to havethe same pump operating between the same level. This means a pump alwaysoperates within a constant volume. The volume is the most importantingredient to calculate flow. If it can not be supplied, the inflow oroutflow can not be calculated, but it is still possible to generatealarms based on a variation of their outflow. In this case, the presentinvention supplies a constant to replace the volume which means theinflow and outflow can not be called as such, but the outflow alarm gate76 and inflow alarm gate 74 still can be used to generate alarms basedon flow variation.

This method could use level status received from the pump station levelsensors (26 and 32) when the pump status converter is not used.

The inflow or outflow calculation could come from an external flowmeter96. This is useful when such external flowmeter 96 is known to be moreaccurate, already installed, or when the volume between level can not bedetermined with accuracy. In these conditions, the Inflow could becalculated if the external flowmeter 96 supplys the Outflow, or theOutflow could be calculated if the external flowmeter 96 supplys theInflow. It could also be used to readjust the Outflow of a pump based onthe difference between the Outflow calculated with the externalflowmeter 96 and the Outflow calculated using the present invention,then applying this difference to the other pumps calculated solely withthe present invention.

FIG. 11 is a block diagram of a pump status conveyer. It describes indetail how the pump status conveyer 52 generates level status from pumpstatus for a pump station having 3 pumps. This model can be used for anynumber of pumps. Level sensors like float switches, ultrasonic orpressure sensors, just to name a few, are installed to start and stopthe pumps in a preset and known sequence when preset levels are reached.Then, if the preset sequence and the pump status is known, it ispossible to know the level at which a pump status is changing withoutbeing connected to any sensor. The level status generated representswhich level is reached and the time at which it is reached. These piecesof information are the basic elements used by volumetric flowmeters.They are known to be accurate if the pump station is not in amaintenance period.

Pump station control panels are built to start and stop the pumps in apredetermined sequence when the liquid level rises and falls. Theoperational sequence can be affected by two external factors: the levelreached and an optional time delay that suspends momentarily thebeginning or the end of an event, which can be a pump start or stop.

The pump status comparator 52 converts pump status signals into levelstatus to determine the level of the liquid in the wet well system andthe time at which the level is reached. An operation sequence memory 80is used for storing an association sequence 82 (expected pumpstatus--level reached) representing, for each level, the pump statusexpected to be received when the level is reached. A comparator 84compares the pump status signal to the expected pump status in theassociation sequence 82, which returns an associated level reached. Alevel memory 86 records the level reached and time of occurrence. Alevel gate operates when the level reached is different than the lastlevel in level memory 86 to replace it with the last level reached whichindicates the level of the liquid in the wet well when the pump statuschanged.

Two things can happen to the liquid level in a pump station: it can riseor fall. For each level, two types of pump status can happen: pumps canstart or stop. In the operation sequence memory 80, the lowest level,the one under which no other events occur, is level 1. The highest, theone over which no other events occur, have the highest number. When theliquid level is rising from level 1 and up, a specific pump status thatrepresents the operation of the pumps is selected for each level. Whenthe liquid level is falling, a specific pump action that represents theoperation of the pumps when the level is falling is selected for eachlevel. Pump action, like Pump #1 starts or Pump #1 stops, can only bechosen once for all the levels because of their specificities. When apump action is not related to a specific pump, like a pump starts orstops, it means it can apply to any of the pumps. This is mostly usedfor pump stations with alternating pumps.

A list of predetermined possible pump status 94 can be used to help theselection.

A predetermined association sequence 82 can be recorded in the operationsequence memory 80 to eliminate the intervention of the user.

A self adjusting operating sequence 92 could read the sequence of thepump status recorded in the data storage memory 60, analyze it, thenrecord the right sequence in the operation sequence memory 80.

FIG. 11 is a schematic of pump operation and level activation withreference to time for a pump station having 3 pumps operating accordingto the association sequence 82 configured in the pump status converter52 of FIG. 10. In most pump stations, pumps alternate to wear themequally. Usually, the inflow is lower than the outflow of a pump, butnot all the time. The outflow of a pump is higher than the inflow whenonly one pump starts, then stops. If the inflow is higher than theoutflow of the pump in operation, the liquid level continues to riseuntil a higher level is reached which starts a second pump. The pumpswill stop at level 1 if the outflow of the pumps combined is higher thanthe inflow. If the inflow is still higher than the outflow of the twopumps in operation, the liquid level continues to rise until a higherlevel is reached which starts a third pump. Pump stations are designedto have a higher outflow than inflow.

Events number 1 to 6 show pumps having individually a higher outflowthan the inflow, and they alternate. Event 7 to 8 shows an inflow higherthan the outflow of the pump, this is why the liquid level 38 is rising.A second pump starts at event 8 and the outflow of the combination ofpumps is higher than the inflow so the level falls between events 8 and9 until level 1 is reached again. Event 10 to 11 shows an inflow higherthan the outflow of the pump, this is why the liquid level 38 is rising.A second pump starts at event 11, but the outflow of the combination ofpumps is still lower than the inflow, so the level continues to riseuntil a third pump starts at event 12 when level 4 is reached. Theoutflow of the combination of pumps is higher than the inflow so thelevel falls between events 12 and 13 to reach level 1 again. Events 14to 16 are the same as 7 to 9. Events 17 to 34 are the same as 1 to 6.

By associating the pump status of FIG. 11 with the settings of theassociation sequence selection 82, we can see that the first pump startsat event 1, level 2 was reached and recorded with its time ofoccurrence. The next pump status is a pump stop at event 2, whichtranslates to a level 1 in the association sequence selection 82. So alevel 1 is recorded with its time of occurrence. The same occurs untilevent 8 when a second pump starts. This translate to level 3 in theassociation sequence selection 82. When all pumps stop at event 9, theassociation sequence selection 82 associates this pump sequence withlevel 1. All the other events use the same procedure.

SUMMARY, RAMIFICATIONS, AND SCOPE

Accordingly, the reader will see that the pump station flowmeter of thisinvention can be installed without being connected to any level sensors,therefore reducing the cost of installation. Furthermore, the pumpstation flowmeter has the advantages of:

reducing the inflow and outflow errors without the use of additional orexisting level sensors;

accurately calculating flows, even when inflow changes rapidly withoutthe use of additional or existing level sensors;

discerning outflow calculation errors from abnormal pump operation;

continuously self adjusting the equation parameters to optimize theaccuracy for each individual station;

identifying when a pump station is in maintenance period;

calculating inflow using a function representing the time changingreality;

generating abnormal pump flow alarms, even without supplying the wetwell geometry or being connected to the level sensors;

calculating inflow and outflow when a pump is continuously running andwhen more than one pump is running.

The pump status converter 52, which is part of this invention can beused to supply to other instruments the level data they need withoutbeing connected to any level sensor. This device can be used in anyinstallation that has a mechanism that changes its state at set levels.This device facilitates the installation of instruments that need toknow the level to operate. Volumetric flowmeters are good examples ofthese instruments. This apparatus reduces installation time of suchinstrument from hours to minutes by reducing or eliminating thenecessary modification of the control panel of the pump station.

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. For example, the flowmeter could be used to calculatethe flow of a solid (like powder) filling a silo at a rate, and amechanical device emptying it at a constant rate when set levels arereached. Another example, the invention could be integrated to a pump togenerate flow variation alarms when the pump is having problems.

Thus, the scope of the invention should be determined by the appendedclaims and their legal equivalents, rather than by the examples given.

What is claimed is:
 1. Apparatus for determining the liquid flowcharacteristics of a wet well system including a wet well, at least onepump connected to the wet well for pumping fluid from the wet well, asource of pump status signals responsive to the at least one pump, and atiming signal generator for generating a timing signal, the apparatuscomprising:(a) pump status converter means responsive to the pump statussignals and the timing signal for converting the pump status signalsinto a level status signal; (b) flow calculating means responsive to thelevel status signal, the timing signal, and a predetermined volumesignal representative of a volume of fluid between predetermined levelsof the wet well for calculating a plurality of filling and emptyingcharacteristics of the wet well; (c) flow rectifying means responsive tosaid flow calculating means for calculating an average emptyingcharacteristic of a plurality of emptying characteristics and forrectifying the plurality of filling and emptying characteristicsresponsive to at least the average emptying characteristic and apredetermined tolerance; (d) variation determining means responsive tosaid flow rectifying means for determining the occurrence of a variationbetween the average emptying characteristic and the predeterminedtolerance, and tagging the level status signal, the timing signal, andthe predetermined volume signal used to calculate the emptyingcharacteristic as being a possible abnormal event; (e) maintenance gatemeans responsive to said variation determining means for operating whena calculated emptying characteristic is higher than a predeterminedmaximum emptying characteristic, for calculating a time of operation ofsaid maintenance gate means and the at least one pump, for calculatingtotal flow through the wet well using the average emptyingcharacteristic multiplied by the time of operation of the at least onepump, and for calculating average filling characteristic by dividing thetotal flow through wet well by the time of operation of said maintenancegate means to thereby generate a maintenance status signal; (f)resetting means responsive to said variation determining means and saidmaintenance gate means for resetting said variation determining meansand untagging the possible abnormal event tagged by said variationdetermining means if no variation between the average emptyingcharacteristic and the predetermined tolerance occurs and responsive tosaid maintenance status signal; and (g) abnormal event gate meansresponsive to said variation determining means and said maintenance gatemeans for operating when a value of said variation determining means ishigher than a predetermined value representing the number of saidpossible abnormal events necessary to become confirmed abnormal eventsand for recalculating the average emptying characteristic from the timeof first tagging the possible abnormal event.
 2. Apparatus as defined inclaim 1, and further including data storing means for storing the pumpstatus and the time at which the pump status changed.
 3. Apparatus asdefined in claim 1, wherein said flow calculating means (58) usesequation Inflow(t)=at³ +bt² +ct+d.
 4. Apparatus as defined in claim 1,wherein said flow calculating means (58) uses equation ##EQU10## 5.Apparatus to convert pump status signals responsive to a pump of a wetwell system into level status for determining the level of a liquid andthe time at which the level is reached in the wet well system, theapparatus comprising:(a) operation sequence memory means for storing anassociation sequence representing each level of a wet well and anexpected pump status to be received when each level is reached; (b)comparator means responsive to said operation sequence memory means forcomparing an actual pump status signal to an expected pump status in theassociation sequence to determine an associated level reached; (c) levelmemory means responsive to said comparator means for storing the levelreached and a time that the level was reached; and (d) level gate meansresponsive to said level memory means operating when the level reachedis different than a last level in level memory means to replace the lastlevel in said level memory means with the level reached which indicatesthe level of the liquid in the wet well when the pump status changed. 6.Apparatus as defined in claim 1, wherein said flow rectifying means alsouses a predetermined proportion.
 7. Apparatus as defined in claim 1,further including an inflow alarm gate means responsive to saidresetting means for operating when said filling characteristics areoutside a maximum variation representing an alarming fillingcharacteristic.
 8. Apparatus as defined in claim 1, further including anoutflow alarm gate means responsive to said resetting means foroperating when said emptying characteristics are outside a maximumvariation representing an alarming emptying characteristic.
 9. Apparatusas defined in claim 8, wherein said filling and emptying characteristicsare replaced by filling and emptying coefficients for generating alarms.10. Apparatus as defined in claim 5, wherein the association sequence ispredetermined to eliminate the intervention of a user of the apparatus.11. Apparatus as defined in claim 1, wherein said flow calculating meanscomprises a first flow calculating means, and wherein the fillingcharacteristic of said first flow calculating means is compared withfilling characteristic calculated by a second flow calculating means toreadjust the filling and emptying characteristics calculated by saidfirst flow calculating means.
 12. Apparatus as defined in claim 1,wherein said flow calculating means comprises a first flow calculatingmeans, and wherein the emptying characteristic of said first flowcalculating means is compared with emptying characteristic calculated bya second flow calculating means to readjust the filling and emptyingcharacteristics calculated by said first flow calculating means. 13.Apparatus as defined in claim 5, wherein the association sequence isselected from a list of predetermined possible events.
 14. Apparatus asdefined in claim 5, further comprisingdelay calculating means responsiveto said comparator means for adding a time difference between a pumpstatus change and the reaching of a level to the time of occurrencebefore it is recorded in said level memory means.
 15. Apparatus asdefined in claim 5, and further including data storing means for storingthe pump status and the time at which the pump status changed. 16.Apparatus as defined in claim 15, wherein the association sequence isself adjusted by a sequence analyzer which reads a sequence of eventsrecorded in said data storing means.